The long term goal of the proposed research project is to develop, at the single membrane level, a complete description of active and passive ion transport in the proximal tubule. This will be accomplished using the new technique (first developed by the principal investigator) of intracellular microelectrode recording from isolated perfused renal tubules. Isolated tubules are used because they possess many advantages over intact kidney preparations for the study of renal electrophysiology and transport; such as the precise control of both the temperature and chemical composition of lumen and bath solutions as well as the reduction of unstirred layers on the basal side of the epithelium during changes in external solutions. Furthermore, the cells of salamander proximal tubules are ideally suited for intracellular microelectrode experiments since they are larger than those of mammalain proximal tubule, and they possess much less basolateral infolding than do mammalian cells. Specifically, microelectrode techniques will be used to study the electrical properties of the basolateral Na-K ATPase as well as the passive properties of both the apical and basolateral cell membranes of the proximal tubule. Intracellular and transepithelial recordings will be performed with both conventional and ion-selective microelectrodes during external ionic replacements and fast temperature transitions. The results of these experiments will be interpreted in terms of an electricial equivalent circuit of the proximal tubule which can ultimately be used to elucidate the mechanisms of ion transport at both the apical and basolateral cell membranes. A detailed knowledge of normal renal transport processes is essential to understanding the physiological consequences of various pathological conditions.